1. Field of the Invention
The present invention relates to a method of forming a minute pattern, and a method of manufacturing a semiconductor device using the same. More particularly, the present invention relates to a method for forming a minute pattern having a nano-size to form a contact hole or a metal wiring that has a size of below about 100 nm, and to a method of manufacturing a semiconductor device using the same.
2. Description of the Related Art
Generally, in semiconductor fabricating processes, a photolithography process includes transcribing a master mask pattern into a photoresist layer on an insulating layer or a conductive layer formed on a substrate. The photoresist layer is patterned to form a photoresist pattern used as a work mask.
In typical photolithography, the photoresist layer is formed on a target layer being patterned such as the insulating layer or the conductive layer. Light such as X-ray or ultraviolet ray is irradiated into the photoresist layer so that the photoresist layer is divided into a high soluble region and a low soluble region. A portion of photoresist layer positioned at the high soluble region is removed to form the photoresist pattern. A target layer pattern for forming an active region, a wiring or a contact hole is formed using the photoresist pattern as the mask.
Photolithography technology has substantially developed, resulting in semiconductor devices with a dynamic random access memory (DRAM) being manufactured in large quantities. The integration degree of the DRAM has increased by about four times in a cycle of about three years. Also, technologies of other memories or logics have constantly developed. According to these trends, the design rule of semiconductor devices has been changed approximately 0.8 μm of 4M DRAM into approximately 0.18 μm of 1G DRAM. To meet the design rule, non-optical lithography technology has been developed.
However, although various kinds of technologies are combined to enhance resolution of a deep ultra violet (DUV) photolithography technology, a minute pattern having a size of below approximately 0.1 μm may be difficult to achieve. To form the minute pattern, diverse technologies, such as a technology using a new light source, have been attempted.
The upgrade of semiconductor fabricating equipment may be a relatively simple approach to overcoming limits of critical dimensions (CD) to form the minute pattern. However, when new equipment is introduced, cost for manufacturing the semiconductor device may increase, and also the processing conditions of the new equipment may have to be accommodated, resulting in increased manufacturing cost.
To overcome resolution limits of the photolithography equipment without introducing new equipment, a thermal flowing process (TFP) and a chemical attached process (CAP) have been introduced.
The TFP includes forming an oxide layer and a photoresist pattern successively on a substrate. The photoresist pattern is thermally treated to form a flowing photoresist pattern. The space of the flowing photoresist pattern is reduced. The TFP may reduce the CD size of the photoresist pattern by controlling processing temperature and time according to characteristics of the photoresist pattern, which includes a photosensitive material. Korean Patent No. 327436 discloses a method of forming minute contact holes using the TPF whereas Japanese Patent Laid-Open Publication No. 1998-83087 provides a method of forming a pattern using the CAP process.
FIGS. 1A and 1B are partially cross sectional views illustrating the method for forming a minute contact according to the above-mentioned Korean Patent.
Referring to FIG. 1A, an insulating layer 12 is formed on a substrate 10. A photosensitive material is coated on the insulating layer 12 by a spin method. The photosensitive material is baked to form a photoresist layer. The photoresist layer is exposed and developed to form a photoresist pattern 14 on the insulating layer.
Referring to FIG. 1B, the photoresist pattern 14 is thermally treated to form a flowing photoresist pattern. The space of the flowing photoresist pattern is gradually reduced. The flowing photoresist pattern may have a curved profile as shown.
However, since the conventional TFP method is fundamentally dependent on the resolution of the photolithography equipment, it is difficult and perhaps impossible to achieve a prescribed resolution. The thermal flowing at a high temperature may deteriorate the uniformity of the photoresist pattern. That is, the fluidity of the photoresist pattern increases in proportion to rising temperature. The photoresist pattern may flow like liquid at a temperature above a glass transition temperature to block the minute pattern, such as the contact hole.
FIG. 2 is a graph illustrating transitions of CD between a DUV photoresist and an i-line photoresist in accordance with temperature variations in the conventional TFP. In FIG. 2, a solid line indicates the DUV photoresist, and a dotted line indicates the i-line (λ=365 nm) photoresist.
Referring to FIG. 2, the CD of the photoresist pattern is constant as temperature is maintained below the glass transition temperature. The CD of the photoresist pattern slowly decreases as the temperature passes just above the glass transition temperature. The CD of the photoresist pattern rapidly decreases as the temperature passes through a point of high temperature above the glass transition temperature.
This means that the property of the photoresist may be rapidly varied at the high temperature above the glass transition temperature. As a result, the TFP may be sensitively dependent on the variations of the high temperature. Since the size of the photoresist pattern may be greatly changed by tiny variations of the temperature, the CD of the photoresist pattern is not easily controlled with variations of the temperature. As shown in FIG. 2, the CD of the DUV photoresist is lowered more rapidly than that of i-line photoresist above the glass transition temperature, that is, the CD of the DUV photoresist is more difficult to control.
FIGS. 3A to 3E are cross sectional views illustrating a method of forming a pattern using a CAP process in accordance with the above-mentioned Japanese Patent Laid Open Publication. Referring to FIG. 3A, an insulating layer 32 is formed on a substrate 30. A photosensitive material is coated on the insulating layer 32 by a spin coating. The photosensitive material is baked at a temperature of about 90 degrees C. to about 110 degrees C. for about 60 seconds to about 100 seconds. The moisture of the photosensitive material is evaporated to form a solid photosensitive material. As a result, a photoresist layer 34 having the solid photosensitive material is formed on the insulating layer 32. The photoresist layer 34 is exposed to an ultra violet ray or an X-ray to divide the layer 34 into an exposure region and a non-exposure region.
Referring to FIG. 3B, the exposure region or the non-exposure region of the photoresist layer 34 is selectively removed to form a photoresist pattern 34a. The space 36 of the photoresist pattern 34a has width a corresponding to a master mask. The width a is limited according to the resolution limit of the equipment.
Referring to FIG. 3C, a hardening material 38 is coated on the photoresist pattern 34a and the insulating layer 32.
Referring to FIG. 3D, the hardening material 38 reacts with the photosensitive material of the photoresist pattern. 34a at boundary surfaces between the hardening material 38 and the photoresist pattern. 34a so that a new material 40 is created. The created material 40 develops between the photoresist pattern 34a and the hardening material. The developed material is connected together to form a hardened layer 42.
Referring to FIG. 3E, the space 36a of the photoresist pattern 34a has a width b shorter than the width A of the space 36a of the photoresist pattern 34a in FIG. 3B due to a thickness of the hardened layer 42. Accordingly, the CD of the photoresist pattern 34a is reduced. The remaining hardening material may be removed by an alkaline solution. The insulating layer 32 is dry etched using the photoresist pattern 34a and the hardened layer 42 as a mask to form a contact hole 32a in the insulating layer 32.
As described above, in the conventional CAP, the hardening material such as a water-soluble polymer is coated on the photoresist pattern. The hardening material reacts with the photosensitive material to form the hardened layer. Accordingly, the CD of the photoresist pattern may be reduced due to the thickness of the hardened layer.
The CAP may be little influenced by the resolution limit of the equipment in contrast to the TFP. Also, because the CAP having the amount attached varying in accordance with the photoresist material and the water-soluble polymer on the photoresist material is stable, the CAP has been widely used for overcoming the resolution limits of the present equipment without introducing new equipment.
However, the CAP may have a limit of the thickness of the hardened layer. When the hardened layer is attached above the limited thickness, the CAP may be unstable and may be not employed in the semiconductor fabricating processes. Furthermore, since the CAP may be dependent on the shape and the density of the photoresist pattern, etc., the CAP may be not stably employed in the semiconductor fabricating processes.